Color filter substrate and fabricating method thereof

ABSTRACT

A color filter substrate includes a substrate, a black matrix that defines cell areas on a substrate and prevents light leakage, a color filter formed in the cell areas defined by the black matrix, and a conductive thin film formed on the rear surface of the substrate for preventing the generation of static electricity, wherein the conductive thin film is formed of a photo-resist containing a conductive material.

This application claims the benefit of the Korean Patent Application No.P2005-0119956 filed on Dec. 8, 2005, which is hereby incorporated byreference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a component of a display device, andmore particularly to a color filter substrate and a fabricating methodthereof. Although the present invention is suitable for a wide scope ofapplications, it is particularly suitable for preventing staticelectricity on the color filter substrate.

2. Description of the Related Art

In general, a liquid crystal display device controls the lighttransmittance of liquid crystal using an electric field across a layerof liquid crystal molecules between two substrates to display a picture.The liquid crystal display device uses cells in an active matrix inwhich a switching device is formed in each of the cells. Liquid crystaldisplay devices are used as display in televisions, computer monitors,office equipment, and cellular phones.

Liquid crystal display devices can be classified as either a verticalelectric field type in which a vertical direction electric field extendsbetween the two substrates or a horizontal electric field type is whicha horizontal direction electric field extends across the surface of oneof the two substrates. The vertical electric field type liquid crystaldisplay device can drive a liquid crystal of TN (twisted nematic) modewith a vertical electric field between a common electrode on an uppersubstrate and a pixel electrode on a lower substrate. The verticalelectric field type liquid crystal display device has an advantage inthat the aperture ratio is high, but on the other hand, it also has adisadvantage in that the viewing angle is narrow, about 90°. Thehorizontal electric field type liquid crystal display device drives aliquid crystal of IPS (in-plane switch) mode with a horizontal electricfield between a pixel electrode and a common electrode, which are formedin parallel on a lower substrate. The horizontal electric field typeliquid crystal display device has an advantage in that the viewing angleis wide, about 160°, but on the other hand, it also has a disadvantagein that the aperture ratio is low.

FIG. 1 is a cross-sectional view representing a horizontal electricfield type liquid crystal display device of the related art. As shown inFIG. 1, the horizontal electric field type liquid crystal display deviceincludes a color filter substrate, a thin film transistor substrate andliquid crystal (not shown) injected into a gap between the substrates.The color filter substrate has a black matrix 4, a color filter 6, anovercoat layer 8, a spacer 13 and an upper alignment film 12sequentially formed on an upper glass substrate 2. Further, atransparent electrode (ITO) 3 for preventing static electricity isformed on the other side of the glass substrate 2 of the color filtersubstrate. The thin film transistor substrate has a thin filmtransistor, a common electrode 10, a pixel electrode 56 and a loweralignment film 52 formed on a lower glass substrate 32.

The black matrix 4 of the color filter substrate overlaps the thin filmtransistors, gate lines (not shown) and data lines (not shown) of thelower glass substrate 32, and defines cell areas where color filters 6are later formed. The black matrix 4 prevents light leakage andincreases contrast ratio by absorbing external light. The color filters6 are formed within the cell areas defined by the black matrix 4. Thecolor filters 6 are red, green, and blue colored filters to realize red,green and blue colors.

The overcoat layer 8 covers a step difference formed by the color filter6 to level the upper substrate 2. The spacer 13 maintains a cell gapbetween the upper and lower glass substrates 2 and 32. The spacer 13 canbe simultaneously formed of the same material as the overcoat layer 8.The upper alignment film 12 is formed on the overcoat layer 8 where thespacer 13 is formed and initially aligns liquid crystal moleculesinterposed between the thin film transistor substrate and the colorfilter substrate in a designated direction. The lower alignment film 52is formed on the passivation film 50, which covers the thin filmtransistor, and initially aligns the liquid crystal molecules interposedbetween the thin film transistor substrate and the color filtersubstrate in the designated direction.

The thin film transistor of the thin film transistor substrate includesa gate electrode 38 formed on the lower glass substrate 32 together withthe gate line (not shown); a semiconductor layer 93, which overlaps thegate electrode 38 with the gate insulating film 34 therebetween; asource electrode 46 and a drain electrode 48. Contact semiconductorlayers 92 reduce the contact resistance between the semiconductor layer93 and each of the source and drain electrodes 46 and 48. In response toa gate signal from the gate line, a thin film transistor applies a pixelsignal from the data line to the pixel electrode 56, which is connectedto the drain electrode 48 through a contact hole in the protectivepassivation film 50.

The common electrode 10, which is a stripe type alternating with a pixelelectrode 22, is simultaneously formed on the lower glass substrate 32along with the gate line. A reference voltage that serves as a referencevoltage upon driving of the liquid crystal 24 is supplied to the commonelectrode 10 through the common line. A horizontal electric field isformed between the pixel electrode 56 to which a pixel signal issupplied through the thin film transistor and the common electrode 10 towhich a reference voltage is supplied through the common line. Thehorizontal electric field causes the liquid crystal molecules, which areinitially arranged in a horizontal direction between the thin filmtransistor substrate and the color filter substrate, to rotate in adesignated direction so as to change the light transmittance through theliquid crystal molecules, thereby realizing a picture.

FIGS. 2A to 2I illustrate a process of forming a color filter substratefor a horizontal electric field type liquid crystal display device ofthe related art. As shown in FIG. 2A, a static electricity preventiontransparent conductive film ITO 3 is formed by a sputtering method onthe glass substrate 2. More specifically, a high RF (DC) power isapplied to a target opposite to the glass substrate 2, both of which arewithin a chamber filled with argon Ar gas. Ar molecules having a highenergy in the plasma formed by the RF (DC) power lose (−) charge andcollide with the target surface in an Ar+ state so that target particlescome out of the target and are deposited onto the glass substrate 2,thereby forming the transparent conductive film (ITO) 3 for preventingstatic electricity buildup, as shown in FIG. 2B.

After forming the transparent conductive film 3 for preventing staticelectricity buildup, the black matrix 4 is formed on the glass substrate2 to prevent light leakage. More specifically, an opaque material isspread on an other side of the glass substrate 2 opposite to the side ofthe glass substrate where the transparent conductive film 3 was formed.The opaque material is an opaque resin or an opaque metal, such aschrome Cr. Next, the opaque material is patterned by a photolithographyprocess using masking and etching processes, thereby forming the blackmatrix 4, as shown in FIG. 2C. Red, green, and blue color filters areformed in cell areas defined by the black matrix after forming the blackmatrix 4.

Specifically, a red photo-sensitive color resin is deposited over theentire surface of the glass substrate 2 on which the black matrix 4 isformed. Next, the red photo-sensitive color resin is patterned by aphotolithography process using masking and etching processes, therebyforming a red color filter R, as shown in FIG. 2D.

After forming the red color filter, a green photo-sensitive color resinis then deposited over the entire surface of the glass substrate 2 onwhich the red color filter R is formed. Then, the green photo-sensitivecolor resin is patterned by a photolithography process using masking andetching processes, thereby forming a green color filter G, as shown inFIG. 2E.

After forming the green color filter, a blue photo-sensitive color resinis deposited over the entire surface of the glass substrate 2 on whichthe red and green color filters R and G are formed. Then, the bluephoto-sensitive color resin is patterned by the photolithography processusing masking and etching processes, thereby forming a blue color filterB so as to complete the color filters 6, as shown in FIG. 2F.

Subsequently, the overcoat layer 8 for providing a planar surface isformed, as shown in FIG. 2G, after forming the R, G, B color filters 6.More specifically, an organic insulating material is coated over theentire surface of the glass substrate 2 on which the color filters 6 areformed. Then, the organic insulating material is patterned by aphotolithography process using a masking and an etching process, therebyforming the overcoat layer 8 having a planar surface over stepdifferences formed by the color filters 6.

After forming the overcoat layer, a spacer 13 is then formed formaintaining a cell gap between the thin film transistor and the colorfilter substrate, as shown in FIG. 2H. More specifically, the sameorganic insulating material used for forming the overcoat layer 8 iscoated over the entire surface of the glass substrate 2 on which theovercoat layer 8 is formed. Then, the organic insulating material ispatterned by a photolithography process using masking and etchingprocesses, thereby forming the spacer 13 to maintain the cell gap, asshown in FIG. 2H.

After forming the spacer 13, an alignment film 12 for initially aligningliquid crystal molecules in a designated direction is formed over thesurface of the glass substrate 2 on which the spacer 13 is formed, asshown in FIG. 2I, thereby completing the color filter substrate.

In the related art, in the case of forming the color filter substrate bythe fabrication process described above, the transparent conductive film(ITO) 3 on the rear surface of the glass substrate 2 is formed by asputtering process, which is a complicated process step that requires alarge amount of time. Further, in the case of forming the color filtersubstrate of the related art with a transparent conductive film 3 on therear surface of the glass substrate 2, there is a problem in that it isimpossible to make the color filter substrate light and thin because theglass substrate 2 can not be etched after the black matrix, the colorfilter, the overcoat layer and the alignment film are formed on theother side of the glass substrate when the transparent conductive film 3is on the rear surface of the glass substrate 2.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a color filtersubstrate and a fabricating method thereof that substantially obviatesone or more of the problems due to limitations and disadvantages of therelated art.

Accordingly, it is an object of the present invention to provide a colorfilter substrate and a fabricating method thereof that has a reducedfabrication time for forming a conductive thin film to prevent staticelectricity on the rear surface of a substrate.

It is another object of the present invention to provide a color filtersubstrate and a fabricating method thereof in which the substrate islight and thin.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a colorfilter substrate includes a substrate, a black matrix that defines cellareas on a substrate and prevents light leakage, a color filter formedin the cell areas defined by the black matrix, and a conductive thinfilm formed on the rear surface of the substrate for preventing thegeneration of static electricity, wherein the conductive thin film isformed of a photo-resist containing a conductive material.

In another aspect, a fabricating method of a color filter substrateincludes forming a black matrix that defines cell areas on a substrateand prevents light leakage, forming color filters in the cell areasdefined by the black matrix, and forming a conductive thin film on therear surface of the substrate for preventing the buildup of staticelectricity, wherein the conductive thin film is formed of aphoto-resist containing a conductive material.

In another aspect, a color filter substrate includes a substrate, ablack matrix that defines cell areas on the substrate and prevents lightleakage, a color filter formed in the cell areas defined by the blackmatrix, and a conductive thin film formed on the rear surface of thesubstrate for preventing the generation of static electricity, whereinthe conductive thin film is formed of a photo-resist containing a carbonnano tube.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1 is a cross-sectional view representing a horizontal electricfield type liquid crystal display device of the related art;

FIGS. 2A to 2I illustrate a process of forming a color filter substratefor a horizontal electric field type liquid crystal display device ofthe related art;

FIG. 3 is a plan view of the color filter substrate for a horizontalelectric field type liquid crystal display device according to anembodiment of the present invention;

FIG. 4 is a cross-sectional view of a color filter substrate taken alongthe line I-I′ of FIG. 3;

FIGS. 5A and 5B are a plan view and a cross-sectional view,respectively, of the color filter substrate in which a black matrix isformed according to an embodiment of the present invention;

FIG. 6A is a plan view of a color filter substrate where the colorfilters are formed according to an embodiment of the present invention;

FIG. 6B is a cross-sectional view of the color filter substrate takenalong the line II-II′ in FIG. 6A;

FIGS. 7A to 7C illustrate a process of forming color filters in cellareas defined by a black matrix;

FIG. 8A is a plan view of the color filter substrate in which theovercoat layer is formed according to an embodiment of the presentinvention;

FIG. 8B is a cross-sectional view of the color filter substrate takenalong the line III-III′ in FIG. 8A;

FIGS. 9A and 9B are a plan view and a cross-sectional view,respectively, of the color filter substrate where an alignment film isformed according to and embodiment of the present invention; and

FIGS. 10A and 10B are a plan view and a cross-sectional view,respectively, of the color filter substrate in which a conductive thinfilm is formed on the rear surface of a glass substrate according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

FIG. 3 is a plan view of a color filter substrate according to anembodiment of the present invention, and FIG. 4 is a cross-sectionalview of the color filter substrate taken along the line I-I′ in FIG. 3.As shown in FIGS. 3 and 4, the color filter substrate according to thepresent invention includes a black matrix 102 formed on the substrate101; color filters 104 formed in cell areas defined by the black matrix102; an overcoat layer 106 which covers a step difference formed by thecolor filters 104 to form a planar surface; an alignment film 108 formedon the overcoat layer 106 to initially align liquid crystal molecules ina designated direction; and a conductive thin film 110 formed on therear surface of the substrate 101 to prevent the generation of staticelectricity. A color filter substrate according to an embodiment of thepresent invention might further include a spacer 107 formed on theovercoat layer 106 to maintain a cell gap into which liquid crystal isfilled.

Herein, the black matrix 102 is formed in a matrix shape on thesubstrate 101 to divide a plurality of cell areas where the colorfilters 104 are to be formed, and at the same time, the black matrix 102acts to prevent light interference between adjacent cell areas. Thus,the black matrix 102 is formed to overlap the gate line, the data lineand the thin film transistor except the pixel electrode of the thin filmtransistor substrate. The black matrix 102 is formed by patterning anopaque metal by a photolithography process and an etching process afterdepositing the opaque metal, such as chrome Cr or CrOx, on the substrate101 to have a line width of 5˜25 μm and a thickness of about 1500˜2000Å. In the alternative, the black matrix 102 might be formed bypatterning an insulating resin by a photolithography process and anetching process after forming the insulating resin on the substrate 101to have a thickness of 1.0˜1.5 μm and a line width of 5˜25 μm.

The color filters 104 are formed in the cell areas defined by the blackmatrix 102. At this moment, a photo-sensitive color resin is patternedby the photolithography process using masking and etching processesafter sequentially spraying the photo-sensitive color resin having red,green and blue colors on the substrate 101 by a pigment spraying method,thereby forming the color filters including a red color filter 104Rrealizing red color, a green color filter 104G realizing green color,and a blue color filter 104B realizing blue color.

The method of realizing the color filters 104 is not limited to thepigment spraying method, which uses the photo-sensitive color resin, andthe color filters 104 can be formed by various methods other than thepigment spraying method, such as a dyeing method, an electrophoreticdeposition method, or a printing method.

The overcoat layer 106 removes the stepped difference formed by thecolor filters 104 by having a planar upper surface such that thealignment film 108 formed by a subsequent process can be made on a flatsurface.

The spacer 107 performs the role of maintaining a cell gap into which aliquid crystal is filled between the thin film transistor and the colorfilter substrate. The spacer 107 can be formed of the same material asthe overcoat layer 106 that overlaps the black matrix 104.

The alignment film 108 is formed on the overcoat layer 106 on which thespacer 107 is formed to initially align liquid crystal molecules in adesignated direction. The alignment film 108 includes a rubbing processof an organic alignment film, such as polyimide, to form an alignmentgroove (not shown) for aligning liquid crystal in the designateddirection.

The conductive thin film 110 is formed on the rear surface of the colorfilter substrate by a coating process using a photo-resist containing aconductive material to prevent the generation of static electricity onthe color filter substrate. The conductive material contained in thephoto-resist is a carbon nano tube. A carbon nano tube is a carbonallotrope made of carbon, which exists in great quantity in the earth,and the carbon nano tube is a material where one carbon is combined withanother carbon atom in a hexagonal honeycomb shape to form a tube shapeand the diameter of the tube is about a nanometer (nm= 1/1,000,000,000meter). The carbon nano tube is similar in electrical conductivity tocopper. The thermal conductivity of carbon nano tube is the best in thenatural world. The strength of carbon nano tube is the same as diamond.

A coating process and a heat treatment process are performed afterpositioning the liquid photo-resist, which contains the carbon nano tubehaving the conductivity described above, on the rear surface of thesubstrate 101, thereby forming the conductive film 110 on the rearsurface of the substrate 101 for preventing static electricity.Hereinafter, in reference to the accompanying drawings, a fabricatingmethod of a color filter substrate for a horizontal electric field typeliquid crystal display device according to an embodiment of the presentinvention will be explained in detail.

FIGS. 5A and 5B are a plan view and a cross-sectional view,respectively, of the color filter substrate in which a black matrix isformed according to an embodiment of the present invention. As shown inFIGS. 5A and 5B, an opaque metal such as chrome Cr or CrOx is depositedon the substrate 101 of color filter substrate with a line width ofabout 5˜25 μm and a thickness of about 1500˜2000 Å. More specifically, aphotolithography process using a masking process and an etching processare performed on the opaque metal, which is deposited on the substrate101, thereby forming a black matrix 102, which defines a plurality ofcell areas in which color filters 104 are later formed. In thealternative, the black matrix 102 might be formed by patterning aninsulating resin by a photolithography process and an etching processafter forming the insulating resin on the substrate 101 to have athickness of 1.0˜1.5 μm and a line width of 5˜25 μm. The black matrix102 also acts to prevent light interference between adjacent cell areasas well as improve the contrast ratio.

FIG. 6A is a plan view of a color filter substrate where the colorfilters are formed according to an embodiment of the present invention,and FIG. 6B is a cross-sectional view of the color filter substratetaken along the line II-II′ in FIG. 6A. After forming the black matrix102 on the substrate 101, the color filter is formed in the cell areas,which are defined by the black matrix, as shown in FIGS. 6A and 6B. Morespecifically, a photo-sensitive color resin is patterned by aphotolithography process using a masking and an etching process aftersequentially spraying the photo-sensitive color resin having red, greenand blue colors by a pigment spraying method on a surface of thesubstrate 101 on which the black matrix 102 is formed, thereby formingthe color filters 104 of a red color filter 104R, a green color filter104G and a blue color filter 104B.

FIGS. 7A to 7C illustrate a process of forming color filters in cellareas defined by a black matrix. More specifically, the redphoto-sensitive color resin is spread by the pigment spraying methodover the entire surface of the substrate 101. Then, the redphoto-sensitive color resin is patterned by a photolithography processusing masking and etching processes, thereby forming the red colorfilter 104R, which shows the red color in the cell areas defined by theblack matrix 102, as shown in FIG. 7A.

After forming the red color filter as described above, the greenphoto-sensitive color resin is spread by the pigment spraying methodover the entire surface of the substrate 101, as shown in FIG. 7B. Then,the green photo-sensitive color resin is patterned by thephotolithography process using masking and etching processes, therebyforming the green color filter 104G, which shows the green color in thecell areas defined by the black matrix 102, as shown in FIG. 7B.

After forming the red and green color filters as described above, theblue photo-sensitive color resin is spread by the pigment sprayingmethod on the entire surface of the substrate 101. Then, the bluephoto-sensitive color resin is patterned by the photolithographyprocess, using masking and etching processes, thereby forming the bluecolor filter 104B, which shows the blue color in the cell areas definedby the black matrix 102 so as to form the color filters 104 on the glasssubstrate 101, as shown in FIG. 7C.

FIG. 8A is a plan view of the color filter substrate in which theovercoat layer is formed according to an embodiment of the presentinvention, and FIG. 8B is a cross-sectional view of the color filtersubstrate taken along the line III-III′ in FIG. 8A. After forming thecolor filters in the cell areas defined by the black matrix, theovercoat layer 106 is formed to have a planar top surface covering thestep differences formed on the substrate 101 by the color filters 104,as shown in FIGS. 8A and 8B.

Referring to FIGS. 8A and 8B, a thermosetting resin, such aspolydimethylsiloxane PDMS, is formed over the entire surface of thesubstrate 101 on which the color filters 104 are formed to cover thestep difference formed by the color filters 104. Thus, the overcoatlayer 106 provides a planar top surface for the later formed alignmentfilm 108. More specifically, a thermosetting resin is provided on thesubstrate 101 and then patterned by a photolithography process usingmasking and etching processes, thereby forming the overcoat layer 106 ona surface of the substrate 101 on which the color filters 104 areformed. The spacer 107, which performs the role of maintaining a cellgap, is then formed on the planar top surface of the overcoat layer.

FIG. 9A is a plan view of the color filter substrate on which thealignment film is formed according to an embodiment of the presentinvention, and FIG. 9B is a cross-sectional view of the color filtersubstrate taken along the line IV-IV′ in FIG. 9A. After forming theovercoat layer 106 and the spacer 107, the alignment film 108 foraligning liquid crystal molecules in the designated direction is formedon the overcoat layer 106. Referring to FIGS. 9A and 9B, an organicalignment film, such as polyimide, is spread over the entire surface ofthe substrate on which the overcoat layer 106 is formed. Then, a rubbingprocess is performed on the organic alignment film, thereby forming thealignment film 108 having alignment grooves, which initially align theliquid crystal molecules in a designated direction.

FIG. 10A is a plan view of the color filter substrate in which aconductive thin film is formed, and FIG. 10B is a cross-sectional viewof the color filter substrate taken along the line V-V′ in FIG. 10A.After forming the alignment film as described above, a conductive thinfilm for preventing static electricity buildup is formed on the rearsurface of the substrate 101. Referring to FIGS. 10A and 10B, theconductive thin film 110 for preventing the static electricity buildupis formed on the rear surface of the substrate 101 by a coating processusing a photo-resist PR containing a conductive material. Morespecifically, a liquid photo-resist PR, containing carbon nano tube as aconductive material, is put on the rear surface of the substrate 101 bya coating process. An etching process can be performed on the substrate101 to make the color filter substrate light and thin before forming theconductive thin film 110 on the rear surface of the substrate 101.

The carbon nano tube is a carbon allotrope made of carbon, and thecarbon nano tube is a material where one carbon is combined with othercarbon atom in a hexagonal honeycomb shape to form a tube shape and thediameter of the tube is about a nanometer (nm= 1/1,000,000,000 meter).The carbon nano tube is similar in electrical conductivity to copper.The thermal conductivity of carbon nano tube is the best in the naturalworld. The strength of carbon nano tube is the same as diamond.

The coating process is performed on the photo-resist by use of arotation chuck (not shown), which holds the substrate 101, therebyspreading the liquid photo-resist containing the conductive materialover the entire rear surface of the substrate 101. Then, the liquidphoto-resist is hardened with a heat treatment, thereby forming theconductive thin film 110 on the rear surface of the color filtersubstrate to prevent the buildup of static electricity.

As described above, the color filter substrate and the fabricatingmethod thereof according to the present invention forms a conductivethin film by using a photo-resist containing the conductive material onthe rear surface of the substrate, thereby providing a quick and easymethod, as compared to the related art, for forming a static electricitybuildup prevention film. Further, embodiments of the present inventionperform the etching process on the color filter substrate before formingthe conductive thin film on the rear surface of the color filtersubstrate for preventing the static electricity buildup such that thecolor filter substrate can be made light and thin.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A color filter substrate, comprising: a substrate having a frontsurface and a rear surface, the rear surface being etched; a blackmatrix that defines cell areas on the front surface of the substrate andprevents light leakage; a color filter formed in the cell areas definedby the black matrix; a conductive thin film formed on the rear surfaceof the substrate for preventing the generation of static electricity; anovercoat layer having a planar surface covering a step difference formedby the color filter and formed of polydimethylsiloxane: and a spacerformed on the overcoat layer for maintaining a cell gap and formed ofthe same material as the overcoat layer, wherein the conductive thinfilm is formed of a photo-resist containing a carbon nano tube; andwherein the conductive thin film is formed by coating a liquidphoto-resist containing the carbon nano tube and heating the coatedliquid photo-resist containing the carbon nano tube.
 2. The color filtersubstrate according to claim 1, further comprising an alignment filmformed on the overcoat layer for aligning liquid crystal molecules in adesignated direction.